Regensburg 2010 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 26: Micro and Nanofluidics I

CPP 26.7: Talk

Wednesday, March 24, 2010, 15:45–16:00, H39

The microscopic origin of surface slip: A neutron scattering study of hexadecane at solid interfaces — •Philipp Gutfreund^1,2, Max Wolff³, Marco Maccarini², Stefan Gerth⁴, and Hartmut Zabel¹ — ¹Ruhr-University Bochum, 44780 Bochum, Germany — ²Institut Laue-Langevin, 38042 Grenoble, France — ³Uppsala University, 75121 Uppsala, Sweden — ⁴University Erlangen-Nuernberg, 91058 Erlangen, Germany

A non-sticking contacting layer of a flowing liquid at solid boundaries, called surface slip, is nowadays observed in a wide range of studies exploring microscopic flow. However, the fundamental origin of boundary slip remains unclear. Different mechanisms were proposed like the formation of a thin depletion layer or a molecular ordering in the liquid near the interface, both changing the interfacial velocity profile and, thus, manifesting in apparent slip. Neutron Reflectometry (NR) and Grazing Incident Neutron Diffraction (GIND) are excellent tools for the investigation of buried boundary layers at solid/liquid interfaces in the nm regime. In this contribution we will show a combined NR and GIND study on in situ sheared hexadecane in contact with differently coated solid interfaces. In the case of an attractive interface a depleted layer is observed which is influenced by shear as well as by temperature. For the low interfacial energy substrate no depletion layer is observed. Thus the depletion layer cannot be the origin of surface slip, as for hexadecane slip was observed in both cases.